If you hit what you're aiming at, not much. Just shoot what you shoot well and never look back. Don't get wrapped up in the caliber debate because as Chad has alluded above, it only opens a can of worms and the arguments never settle anything.
Here is an excerpt from a www.policemag.com
"The ultimate stopping power rests with your training with your weapon system. Accurate hits in any reasonable caliber will "stop" a person if that person has experienced enough brain or spinal cord damage to interrupt regular neurologic impulses from reaching vital areas of the body or the person has hemorrhaged enough blood to lower his or her blood pressure where the brain no longer is able to function well. You can also stop a person if a major bone shatters after a bullet injures it, but does that stop the fight?
Stopping power is a marketing tool and should be dropped from our discussions of ballistic performance until such time as ammunition effectiveness is measured by more means than just the results of gelatin and barrier tests. When ammunition companies or regulatory agencies begin to use computer simulations, simulant tests, animal models, autopsy results, and trauma surgeon operation reports with hospital summaries to determine the effectiveness of their products, then we will know which ammunition can be labeled as having the "best stopping power." And this claim will be based on scientific data rather than incomplete ballistic testing.
Until then, shot placement with any commercially available ammunition will offer you the best chance of maximizing your duty ammunition's stopping power."
The full article can be found here